LONDON - Britain has the longest limit for holding terror suspects without formal charge of any comparable democracy, a rights group said Monday.

The Liberty group surveyed 15 countries, and found Britain's 28-day holding period was the lengthiest, The Guardian reported.

By comparison, the group noted terror suspects are given a 48-hour window in the United States, and seven and a half days in Turkey.

In light of some calls in Britain to extend the no-charge detention period even further, Liberty Director Shami Chakrabarti wrote an appeal to Prime Minister Gordon Brown.

"I have every hope that this new, damning evidence, alongside proportionate alternatives to lengthy pre-charge detention, will persuade him to think again," Chakrabati wrote.

Scotland Yard Commissioner Ian Blair is in favor of lengthier detentions to allow for more investigation, and has said in countries such as France and Germany, judicial oversight allows people to be detained for years without being charged.